The overall goal is to elucidate the molecular mechanism of excitation-contraction coupling in normal and diseased cardiac muscle. Based upon the unique distribution of the ryanodine receptor (RyR) mutations reported in some cardiac diseases and the pilot studies, the investigator postulates that these mutable domains constitute interacting domain pairs, and that zipping of such domain pairs closes the calcium channel while unzipping opens the channel. Weakening of the inter-domain interaction will cause an increased tendency of domain unzipping, and hence of channel-opening; this leads to the general syndrome of cardiac disease (i.e. increased cytoplasmic Ca 2+ and cardiac injury). According to the investigator's recent studies, a group of peptides corresponding to various regions of the RyR (designated as domain peptides) serves as a powerful tool to identify and characterize key domains involved in Ca 2+ channel regulation. Such domain peptides will be used to mimic the same type of channel hyper-activation phenomena that occur in diseased channels. Mutated domain peptides will be used as a negative control to test the physiologic significance of the observed hyper-activation effect of the peptides. Localizing the regions of the RyR to which these domain peptides bind by means of site-directed fluorescence labeling will identify the key domain pair. By using a fluorescence probe that has been incorporated into the critical site of the domain pair, the investigator proposes to monitor the zipping/unzipping action of the interacting domains. The investigator and his collaborators will then examine the effects of domain peptides on the cardiac channel at levels ranging from the single molecule (single channel measurements) to the whole cell system (skinned cardiac fibers). Further, in collaboration with a group of researchers working on channel dysfunction in a cardiac hypertrophy animal model, the investigator will examine how the domain zipping/unzipping action is altered in this disease model and how one can pharmacologically control the altered domain and channel functions. The new information derived from this program will permit a better understanding of the fundamental mechanism of cardiac calcium channel regulation as well as the pathogenic mechanism of Ca 2+ channel dysfunction occurring in some cardiac diseases. This program will also provide one with new clues for the method of treatments of diseased cardiac RyR channels.